1. Field of the Invention
The present invention relates to a sliding mechanism of an encoder and a manufacturing method thereof for detecting a displacement between two objects which are arranged so that they can be moved relative to each other.
2. Description of the Related Art
Concerning the encoder, there are provided various types of encoders such as a photoelectric type encoder, electrostatic capacity type encoder and magnetic type encoder. In any type encoder, it is necessary to form a predetermined gap for preventing abrasion between a scale and a detecting section which detects a displacement of the scale. In order to obtain a high intensity of signal, it is desired that this gap is reduced as minute as possible. Conventionally, as a method of forming the above minute gap, a bearing mechanism or sliding roller mechanism has been adopted.
However, in the case of a mechanical construction such as a bearing mechanism, the assembling work becomes complicated. Therefore, the mechanical construction is not appropriate for mass production. Recently, the resolution of a scale has reached a very minute order such as sub-microns. According to that, it becomes necessary to reduce the gap formed between the scale and the detecting section to less than several tens xcexcm. It is very difficult for the mechanical construction such as a bearing mechanism to attain such a minute gap.
It is an object of the present invention to provide a sliding mechanism of an encoder and a manufacturing method thereof capable of obtaining a minute gap by a simple manufacturing process so that the sliding mechanism of an encoder can be appropriately used for mass production.
A sliding mechanism of an encoder of the present invention comprises: a scale having a predetermined reference grating is formed; a detecting section, which is arranged being opposed to the scale at a predetermined interval and can be relatively displaced with respect to the scale, for detecting a displacement distance or a displacement direction with respect to the scale; a sliding rail formed on one of the scale and the detecting section in the displacement direction of the detecting section; and a sliding plating film formed on the other of the scale and the detecting section so that the film can be contacted with the sliding rail, the sliding plating film sliding on the sliding rail when the detecting section is displaced, wherein the sliding rail and the sliding plating film are a compound plating film on which a self lubricating substance is dispersed by an electroless compound plating. In this case, it is preferable that the sliding rail is formed on the scale and the sliding plating film is formed on the detecting section. Further, it is preferable that the self lubricating substance is selected from at least one of polytetrafluoroethylene resin, silicon carbide and boron nitride.
According to the present invention, by the self lubricating property of the self lubricating substance, a friction between the sliding rail and the sliding plating film can be reduced. Therefore, the detecting section can be smoothly slid with respect to the scale. Further, the sliding rail and the sliding plating film are generated by the technique of electroless plating. Accordingly, when a plating bath time of the electroless plating is appropriately adjusted, the thickness of the sliding rail and the sliding plating film can be accurately controlled. Therefore, compared with the conventional mechanical construction such as a bearing mechanism or sliding roller mechanism, an adjustment of the minute gap between the scale and the detecting section can be very easily executed according to the construction of the present invention. Further, it becomes unnecessary to conduct maintenance work such as feeding lubricant, that is, maintenance can be made easily.